Seminar Topics

CAPTCHA

A CAPTCHA is a type of challenge response test used in computing to determine whether the user is human. “CAPTCHA” is an acronymfor “completely automated public turing test to tell computers and humans apart”. A CAPTCHA involves one computer (a server) which asks a user to complete a test. While the computer is able to generate and grade the test, it is not able to solve the test on its own.

Because computers are unable to solve the CAPTCHA, any user entering a correct solution is presumed to be human. A common type of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a CAPTCHA is sometimes described as reverse turing test .